<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <textarea v-model="val" cols="30" rows="10"></textarea>
        <div v-html="mark"></div>
    </div>
    
</body>
</html>
<script src="https://cdn.bootcdn.net/ajax/libs/marked/1.2.7/marked.min.js"></script>
<script src='https://cdn.jsdelivr.net/npm/vue@2.6.14/dist/vue.js'></script>

<script>
    let vm = new Vue({
        el:"#app",
        data:{
            val:"# 一级标题",

        },
        computed:{
            mark(){
                console.log(this.val)
                console.log(marked(this.val))
                return marked(this.val)
            }
        }
    })
</script>